As one among image display systems using a display device such as a projector, liquid crystal display, etc., there has been the interactive white board (IWB; Interactive White board) system. The IWB system is a system that is capable of manipulating the display image on the display device by using an input device such as an electronic pen or the like. In the IWB system, when the user performs a drawing on the display screen of the display device using an input device, the position pointed by the input device in accordance with the drawing is detected, and based on the detection result an image corresponding to the drawing (e.g., the trace of the position pointed by the input device) is displayed in a superimposed manner on the display image of the display device. According to the IWB system, the user is able to add text and patterns on the displayed image as if it were handwritten.
In use of the IWB system, there are cases where multiple users perform drawing by using different input devices. In this case, it is preferable that images drawn by different users can be discriminated by displaying different colors or by other methods.
As a method of discriminating images drawn by multiple users, Patent Document 1 (JP2013-164489A) discloses a method in which a plurality of input devices each are assigned with unique ID information so as to detect the ID information of the input device being used for drawing when a drawing is performed. According to this method, since each input device used for drawing can be identified even when multiple users perform drawing by using different input devices, it is possible to discriminate the image corresponding to drawing made by each input device, by showing display with different colors and/or different line types or any other method.
There has been another method in which the display screen of the display device is divided (into left and right parts, for example) so as to display images corresponding to drawings in different areas, in different modes. When in the IWB system multiple users (two users, for example) perform drawing, it is mostly expected that one user will stay on the right side of the display device and performs drawing mainly on the right side of the display image area while the other user will stay on the left side of the display device and performs drawing mainly on the left side of the display image area. In this case, it is possible to discriminate images corresponding to drawings of multiple users by dividing the display image into left and right areas and displaying the image corresponding to the drawing to the left area and the image corresponding to the drawing to the right area in different modes.